The invention relates to a method for covering a first layer or layer sequence situated on a substrate with an additional second layer by sputtering deposition.
In semiconductor technology for the production of integrated circuits in single or multiple layers which are situated on a semiconductor substrate, such as for the purpose of contacting semiconductor regions, windows are etched by a wet-chemical process. Subsequently, additional layers, for example metal layers, are deposited as conductor paths onto the layer provided with a structure in the aforementioned manner. Such methods are utilized, for example, in the Si-Si-gate process in which a silicon dioxide layer, then a polycrystalline silicon layer, and subsequently another silicon dioxide layer are deposited on a silicon substrate, and in the further process contact windows are etched through to the silicon substrate through this multiple layer. Under etching (or sub-etching) structures are formed during the etching of such layer sequences due to the different etching rates of the individual layers. This leads to difficulties in subsequent coating processes in which, for example, a contact hole which is produced is filled and coated with a conductor path layer, because the deposited conductor path layer can tear off at the under-etchings. Such under-etchings can additionally lead to more difficulties since residues of the etching compound and thus contaminants settle therein which cannot completely be removed from the very small hollow spaces. Such etching compound residues can attack subsequently mounted layers and lead to electrical instabilities, for example, by means of Na.sup.+ ions and can thus lead to the breakdown of individual components, particularly in integrated circuits. Therefore, etched structures without such under-etchings and having a slope angle of approximately 45.degree. are desirable.
In accordance with a known method, allowances can be made for the overhanging edges of such under-etchings or sub-etchings when the under-etching can be covered by means of a subsequent "flowglass" coating. In such a "flowglass" coating, a glass layer, for example a phosphorus glass layer, is deposited before etching of the structures. During the etching process the glass layer is more strongly attacked than the SiO.sub.2 layer lying underneath. This leads to an oblique surface of the SiO.sub.2 structures without an interfering under-etching. After the etching of the structures, for example of the contact holes, the phosphorus glass layer is caused to melt and flow with the aid of a heat treatment whereby the edges of the etching structures are utilized. However, the disadvantage of this technique is that in structures of very small dimensions, for example, in the production of contacts and conductor paths having a width of 2.5 .mu.m and a reciprocal or mutual distance of such magnitude, a sufficient edge covering can no longer be guaranteed. A method is desirable in which, simultaneously with the mounting of the additional layer or layers such as the conductor paths or contact metal layers, the under-etching structures, unavoidable with wet-chemical etching, are filled, or overhanging flanks of such sub-etching structures are removed.